Device and method to measure mass loss rate of an electrically heated sample

Abstract

A device and a method for measuring the mass loss rate of a sample of combustible material placed on a mass-sensitive platform. The material has been formed into a block through which a heating wire has been inserted that thermally degrades the block when an electric current is passed through the embedded wire. Because the terminal ends of the embedded wire deform when heated, attachments that supply the current to these terminals exert spurious forces on the block resulting in inaccurate mass measurements. To eliminate these forces, the terminal ends of the heating wire are connected to high conductivity leads that are dipped into electrically insulated reservoirs of a conductive fluid, typically mercury, to which a power supply provides a potential difference. As the terminal ends of the heating wire deform under the resulting current, the leads are free to move in the conductive fluid without exerting any forces on the block, allowing the true mass loss rate of the sample to be measured.

I claim:  
     
       1. An apparatus for measuring the mass loss of a sample undergoing thermal decomposition caused by an electric current introduced into said sample through a first and a second conductive lead projecting therefrom, said apparatus comprising: 
       a. a mass-sensitive platform supporting said sample, said platform providing a signal indicating the mass of the sample supported;  
       b. a first reservoir adjacent to said platform and containing a conductive fluid;  
       c. a second reservoir adjacent to said platform and containing a conductive fluid;  
       d. said first and second reservoirs electrically insulated from each other;  
       e. said first conductive lead inserted into said conductive fluid contained in said first reservoir such that said first conductive lead is in contact only with said conductive fluid;  
       f. said second conductive lead inserted into said conductive fluid contained in said second reservoir such that said second conductive lead is in contact only with said conductive fluid;  
       g. means for accepting a potential difference between the conductive fluid in said first reservoir and the conductive fluid in said second reservoir such that an electrical current may flow from the conductive fluid in said first reservoir to said first conductive lead into said sample and thence from said second conductive lead into said conductive fluid contained in said second reservoir.  
     
     
       2. The apparatus as in  claim 1  wherein said conductive fluid is mercury. 
     
     
       3. The apparatus as in  claim 1  wherein said conductive fluid is tin, and said first and second reservoirs are maintained at a temperature at or above the melting point of tin. 
     
     
       4. The apparatus as in  claim 1  wherein said conductive fluid is bismuth, and said first and second reservoirs are maintained at a temperature at or above the melting point of bismuth. 
     
     
       5. An apparatus for measuring the mass loss of a sample undergoing thermal decomposition caused by an electric current introduced into said sample through a first and a second conductive lead projecting outward therefrom, said apparatus comprising: 
       a. a mass-sensitive platform for supporting said sample, said platform providing a signal indicating the mass of the sample supported;  
       b. a first high conductivity wire electrically connected to and projecting downward from said first conductive lead;  
       c. a second high conductivity wire electrically connected to and projecting downward from said second conductive lead;  
       d. a first reservoir adjacent to said platform and containing a conductive fluid;  
       e. a second reservoir adjacent to said platform and containing a conductive fluid;  
       f. said first and second reservoirs electrically insulated from each other;  
       g. said first high conductivity wire inserted into said conductive fluid contained in said first reservoir such that said first high conductivity wire is in contact only with said conductive fluid;  
       h. said second high conductivity wire inserted into said conductive fluid contained in said second reservoir such that said second high conductivity wire is in contact only with said conductive fluid;  
       i. means for accepting a potential difference between the conductive fluid in said first reservoir and the conductive fluid in said second reservoir such that an electrical current may flow from the conductive fluid in said first reservoir to said first high conductivity wire into said first conductive lead and into said sample and thence from said second conductive lead into said second high conductivity wire into the conductive fluid contained in said second reservoir.  
     
     
       6. The apparatus as in  claim 5  wherein said conductive fluid is mercury. 
     
     
       7. The apparatus as in  claim 5  wherein said conductive fluid is tin and said first and second reservoirs are maintained at a temperature at or above the melting point of tin. 
     
     
       8. The apparatus as in  claim 5  wherein said conductive fluid is bismuth and said first and second reservoirs are maintained at a temperature at or above the melting point of bismuth. 
     
     
       9. A method for measuring the mass loss rate of a sample undergoing thermal decomposition caused by an electric current flowing through an embedded heating wire terminating in a first and a second conductive lead projecting from said sample, said method comprising the steps of 
       a. supporting said sample on a mass-sensitive platform that provides a measurement of the mass of said sample;  
       b. positioning a first reservoir containing a conductive fluid adjacent to said mass-sensitive platform;  
       c. positioning a second reservoir containing a conductive fluid adjacent to said mass-sensitive platform;  
       d. electrically insulating said first and second reservoirs from each other;  
       e. dipping said first conductive lead into said conductive fluid in said first reservoir such that no part of said first conductive lead touches any part of said first reservoir;  
       f. dipping said second conductive lead into said conductive fluid in said second reservoir such that no part of said conductive lead touches any part of said second reservoir;  
       g. providing a voltage difference to said conductive fluid in said first reservoir and said conductive fluid in said second reservoir; and,  
       h. measuring the mass of said sample as a function of time.  
     
     
       10. The method as in  claim 9  wherein said conductive fluid is mercury. 
     
     
       11. The method as in  claim 10  wherein the conductive fluid is tin and said first and second reservoirs are maintained at a temperature at or above the melting point of tin. 
     
     
       12. The method as in  claim 10  wherein the conductive fluid is bismuth and said first and second reservoirs are maintained at a temperature at or above the melting temperature of bismuth. 
     
     
       13. A method for measuring the mass loss rate of a sample undergoing thermal decomposition caused by an electric current introduced into said sample through a first and a second conductive lead projecting therefrom, said method comprising the steps of: 
       a. supporting said sample on a mass-sensitive platform that provides a measurement of the mass of said sample;  
       b. positioning a first reservoir containing a conductive fluid adjacent to said mass-sensitive platform;  
       c. positioning a second reservoir containing a conductive fluid adjacent to said mass-sensitive platform;  
       d. electrically insulating said first and second reservoirs from each other;  
       e. dipping said first conductive lead into said conductive fluid in said first reservoir such that no part of said first conductive lead touches any part of said first reservoir;  
       f. dipping said second conductive lead into said conductive fluid in said second reservoir such that no part of said conductive lead touches any part of said second reservoir;  
       g. providing a voltage difference to said conductive fluid in said first reservoir and said conductive fluid in said second reservoir; and,  
       h. measuring the mass of said sample as a function of time.  
     
     
       14. The method as in  claim 13  wherein said conductive fluid is mercury. 
     
     
       15. The method as in  claim 13  wherein said conductive fluid is tin and said first and second reservoirs are maintained at a temperature at or above the melting point of tin. 
     
     
       16. The method as in  claim 13  wherein said conductive fluid is bismuth and said first and second reservoirs are maintained at a temperature at or above the melting point of bismuth. 
     
     
       17. A method for measuring the mass loss rate of a sample undergoing thermal decomposition supported by an electric current introduced into said sample through a first and a second conductive lead projecting outward therefrom, said method comprising the steps of: 
       a. supporting said sample on a mass-sensitive platform that provides a measurement of the mass of said sample;  
       b. positioning a first reservoir containing a conductive fluid adjacent to said mass-sensitive platform;  
       c. positioning a second reservoir containing a conductive fluid adjacent to said mass-sensitive platform;  
       d. electrically insulating said first and second reservoirs from each other;  
       e. electrically connecting a first high conductivity wire to said first conductive lead such that said first high conductivity wire projects downward from said first conductive lead;  
       f. dipping said first high conductivity wire into said conductive fluid in said first reservoir such that no part of said first high conductivity wire touches any part of said first reservoir;  
       g. dipping said second high conductivity wire into said conductive fluid in said second reservoir such that no part of said high conductivity wire touches any part of said second reservoir;  
       h. providing a voltage difference between said conductive fluid in said first reservoir and said conductive fluid in said second reservoir; and,  
       i. measuring the mass of said sample as a function of time.  
     
     
       18. The method as in  claim 17  wherein said conductive fluid is mercury. 
     
     
       19. The method as in  claim 17  wherein said conductive fluid is tin and said first and second reservoirs are maintained at a temperature at or above the melting point of tin. 
     
     
       20. The method as in  claim 17  wherein said conductive fluid is bismuth and said first and second reservoirs are maintained at a temperature at or above the melting point of bismuth.